Osteoporosis is a pathologic state or disease involving some symptom or risk due to quantitative bone reduction exceeding a certain degree. Major symptoms are spinal kyphosis, fractures of dorsolumbar bones, vertebral centra, femoral necks, lower end of radius, ribs, upper end of humerus, and others. In normal bone tissue, bone breakdown occurs constantly, but there is good balance between bone formation and resorption; osteoblasts and osteoclasts play key roles in bone formation and bone resorption, respectively. Upon deterioration of this balance, bone resorption surpasses bone formation, resulting in quantitative bone reduction. Drugs suppressing bone resorption are therefore expected to serve well in preventing and treating osteoporosis. Traditionally, bone resorption-suppressing agents such as estrogens and calcitonin have been used to treat osteoporosis. However, these therapeutic agents fail to achieve satisfactory effect in some cases, due to subject limitations or uncertain efficacy. There is therefore need of a new prophylactic/therapeutic method for accentuated bone resorption.
It has recently been shown that cathepsin L, a protease secreted by osteoclasts in the process of bone resorption, is involved in the decomposition of collagen, a bone supporting protein. Epoxysuccinic acid derivatives, such as those disclosed in Japanese Patent Unexamined Publication Nos. 304074/1990, 304075/1990 and 304085/1990 appear to exhibit cathepsin L inhibitory action. However, as disclosed in the above patent publications, these epoxysuccinic acid derivatives inhibit not only cathepsin L but also other proteases.
Traditionally, leupeptin and antipain have been known to inhibit protease activity, and various compounds have been synthesized as aldehyde derivatives from amino acids. For example, acetyl-Leu-Leu-tryptophanal, acetyl-Leu-Leu-phenylalaninal etc. are disclosed as chymotrypsin inhibitors in Biochemical and Biophysical Research Communications, Vol. 49, p. 343 (1972). Peptide-derived phenylalaninal and tryptophanal derivatives are disclosed as chymotrypsin inhibitors and myodystrophy remedies in PCT Int. Appl. WO 8400365. Also, PCT Int. Appl. WO 9214696 and PCT Int. Appl. WO 9204045 disclose the anti-HIV activity of peptide-derived phenylalaninal derivatives and the CCK (cholecystokinin) antagonist activity of N-acyltryptophanal, respectively. EP-A2-0 504 938 discloses a use for prophylaxis or treatment of bone disease of peptidic aldehyde derivatives based on their hypocalcemic effect. However, these references do not disclose peptide derivatives useful in the inhibition of cathepsin L activity.
It would be desirable to have an agent that can be used to suppress bone resorption.
It would also be desirable to have an agent that is capable of inhibiting cathepsin L activity without significantly inhibiting other proteases.
It would further be desirable to have a method that can be used to readily screen and select compounds that affect bone resorption.